Aircraft supplemental electrical power systems and methods

ABSTRACT

Supplemental power systems for aircraft are described. One example is a power conversion system for an electrical power system in a twin engine aircraft having a first generator and a second generator is described. The power conversion system includes a first branch, a second branch, and a selector. The first branch has a first input, a first power converter, and a first output configured for coupling to an aircraft electrical distribution system. The second branch includes a second input, a second power converter, and a second output configured for coupling to the aircraft electrical distribution system. The selector is coupled between the first branch and the second branch. The selector is configured to selectively connect the first generator to the first branch or to the first and second branches. The selector is also configured to selectively connect the second generator to the second branch or the first and second branches.

BACKGROUND

The present disclosure relates generally to aircraft electrical powersystems, and more particularly to supplemental electrical power systemsand methods for twin engine aircraft.

Modern aircraft include a large number of electrically powered loads.Electrically powered loads include, for example, cabin services,avionics, communications systems, fuel pumps, galley refrigeration,fans, lighting, etc. To provide electrical power for the various loads,an aircraft typically includes at least one generator mechanicallycoupled to at least one of the aircraft's engine(s). The generator'soutput electrically powers the aircraft's power distribution system.

In some know twin engine aircraft, each engine has a generator coupledto its gearbox. The main generator may contain a transmission that helpsensure that the generator is driven at a substantially constant speed toproduce a substantially constant output. The alternating current (AC)outputs of the two main generators are coupled to the power distributionsystem to power the aircraft's electrically powered loads. The maingenerators are sized to be capable of providing enough power for all ofthe electrically powered loads. A backup generator is also coupled toeach of the two engines. The backup generators are used to back up themain generators during abnormal conditions. The backup generators mayproduce a variable frequency output that may be converted to a fixedfrequency. In this case, the variable frequency output power of a backupgenerator is rectified and supplied to a direct current (DC) bus. The DCbus is connected to an inverter that produces a substantially fixedfrequency and magnitude AC output from the DC input. The AC output ofthe inverter may then be used to power at least some of the electricallypowered loads. The backup generators may be required to comply withvarious regulations, but the backup generators are typically not usedunder normal operating conditions.

BRIEF DESCRIPTION

In one aspect, a supplemental electrical power system for use in a twinengine aircraft is described. The twin engine aircraft has a first and asecond main generator driven by a first and second engine. The first andsecond main generators are coupled to provide power to a powerdistribution system in the aircraft. The supplemental electrical powersystem includes a first supplemental generator driven by the firstengine, a second supplemental generator driven by the second engine, afirst power converter, a second power converter, and a selector. Thefirst power converter has a first input and a first output. The firstinput is coupled to the first supplemental generator. The first outputis coupled to the power distribution system. The second power converterhas a second input and a second output. The second input is coupled tothe second supplemental generator. The second output is coupled to thepower distribution system. The selector is connected between the firstand second power converters to permit selective connection of the firstand second inputs.

In another aspect, a power conversion system for an electrical powersystem in a twin engine aircraft having a first generator and a secondgenerator is described. The power conversion system includes a firstbranch, a second branch, and a selector. The first branch has a firstinput, a first power converter, and a first output configured forcoupling to an aircraft electrical distribution system. The secondbranch includes a second input, a second power converter, and a secondoutput configured for coupling to the aircraft electrical distributionsystem. The selector is coupled between the first branch and the secondbranch. The selector is configured to selectively connect the firstgenerator to the first branch or to the first and second branches. Theselector is also configured to selectively connect the second generatorto the second branch or the first and second branches.

In another aspect, an electrical power system for use in a twin engineaircraft having a first engine, a second engine, and a plurality ofelectrically powered loads is described. The electrical power systemincludes a first main generator, a second main generator, a firstsupplemental generator, a second supplemental generator, and a powerconversion system. The first main generator is driven by the firstengine and coupled to a power distribution system. The second maingenerator is driven by the second engine and coupled to the powerdistribution system. The first and second main generators have acombined output power less than a maximum power requirement of theplurality of electrically powered loads. The first supplementalgenerator is driven by the first engine. The second supplementalgenerator is driven by the second engine. The first and secondsupplemental generators have a combined supplemental output powergreater than a difference between the combined output power of the firstand second main generators and the maximum power requirement of theplurality of electrically powered loads. The power conversion system iscoupled to the first and second supplemental generators. The powerconversion system is configured to selectively couple power from thefirst and second supplemental generators to the power distributionsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a one-line diagram of an exemplary electrical power system fora twin engine aircraft.

FIG. 2 is a mechanical diagram of a portion of the electrical powersystem shown in FIG. 1.

FIG. 3 is a supplemental electrical power system for use in theelectrical power system shown in FIG. 1.

FIG. 4 is another supplemental electrical power system for use in theelectrical power system shown in FIG. 1.

FIG. 5 is a flow diagram of an exemplary aircraft production and servicemethodology.

FIG. 6 is a block diagram of an exemplary aircraft.

DETAILED DESCRIPTION

The present disclosure relates generally to aircraft electrical powersystems. More particularly, this disclosure relates to supplementalelectrical power systems for twin engine aircraft.

The exemplary power systems described herein include a main power systemand a supplemental power system. The supplemental power system mayfunction as both a backup power system for the main power system and asupplement to the main power system. Thus, the example implementationsmay allow smaller main power generators to be used in aircraft. Reducingthe size of the main power generators reduces the weight of the aircraftand redistributes the load on the aircraft's engines, and therebyincreases the efficiency of the aircraft.

FIG. 1 is a one-line diagram of an electrical power system 300 for atwin engine aircraft (not shown). FIG. 2 is a simplified diagram of themechanical components of a portion of electrical power system 300. Withreference to FIG. 1, power system 300 includes a main power systemincluding a first main generator 302, a second main generator 304, afirst distribution bus 306, and a second distribution bus 308. The mainpower system provides electrical power from first main generator 302 andsecond main generator 304 to loads 310 and 310A via busses 306, 308,342, and 344. First and second generators 302 and 304 are connected tofirst and second busses 306 and 308 through generator circuit breakers312. Although the exemplary implementation is a three phase system, forclarity FIG. 1 shows conductors for a single phase of electricity. Otherimplementations may include any number of phases, including a singlephase or two phases.

First main generator 302 is mechanically coupled to a first engine 314and second main generator 304 is mechanically coupled to a second engine316. FIG. 2 is a simplified diagram of the mechanical connection offirst main generator 302 to a gearbox 317 of first engine 314. Secondmain generator 304 is similarly connected to second engine 316 via agearbox 317. Main generators 302 and 304 may be fixed or variablefrequency generators when driven by first and second engines 314 and316. In an example implementation, main generators 302 and 304 aremechanically coupled to gearboxes 317 of first and second engines 314and 316 via mechanical transmission systems (not shown) that rotate maingenerators 302 and 304 at a substantially constant speed regardless ofthe rotational speed of first and second engines 314 and 316.

First and second distribution buses 306 and 308 are connected to loads310 by load conductors 318 and load circuit breakers 320. In the exampleimplementation, first distribution bus 306 and second bus 308 eachprovide power to different loads 310. First main generator 302 generallyprovides power to loads 310 that are connected to first distribution bus306, and second main generator 304 generally provides power to loads 310that are connected to second distribution bus 308. First distributionbus 306 and second distribution bus 308 are selectively connectable viabus tie breakers 322 and conductors 324 to permit either or both maingenerators 302 and 304 to provide power to both of first and seconddistribution bus 306 and 308.

An auxiliary generator 326 is mechanically coupled to and driven by anauxiliary engine 328. In the example implementation, auxiliary engine328 operates at a substantially constant speed and is directly (i.e.,without a mechanical transmission system) connected to auxiliarygenerator 326. Auxiliary engine 328 drives auxiliary generator 326 at asubstantially constant speed to produce a substantially constant output.The AC output of auxiliary generator 326 is selectively connectable tofirst and/or second bus 306 or 308 via an auxiliary power breaker 330and bus tie breakers 322.

First and second distribution bus 306 and 308, bus tie breakers 322,conductors 318 and 324, and load circuit breakers 320 form part of apower distribution system for the aircraft. External power may beconnected to the power distribution system through external power ports332 and their associated external power contactors 334.

Power system 300 includes a supplemental power system including a firstsupplemental generator 336, a second supplemental generator 338, a powerconversion system 340, a first transfer bus 342, and a second transferbus 344. Typically, the supplemental power system provides electricalpower to supplement the power provided by the main power system and toback up the main power system. In the example implementation, thesupplemental power system is configured (e.g., sized, rated, etc.) toprovide sufficient power to power loads 310A (which may be referred toas a subset of all loads). Thus, the supplemental power system can backup the main power system and provide power to loads 310A if first and/orsecond main generator 302 and/or 304 is unable to provide power to firsttransfer bus 342 and/or second transfer bus 344. In someimplementations, loads 310A are important loads, such as navigationsystems, fuel pumps, etc. In such implementations, first and secondsupplemental generators 336 and 338 may operate less than continuously(e.g., only when one of first and second main generators 302 and 304 isnot outputting power).

First and second transfer buses 342 and 344 are connected to loads 310Aby load conductors 318A and load circuit breakers 320A. In the exampleimplementation, first distribution bus 306 and second distribution bus308 provide power to transfer buses 342 and 344 through power contactors348 and 350 during normal operation. Upon a loss of power to firstdistribution bus 306, contactor 348 is opened and converter circuitbreaker 346 is closed, allowing first transfer bus 342 to be poweredfrom the supplemental power system converter 340. Upon loss of power tosecond distribution bus 308, contactor 350 is opened and convertercircuit breaker 346 is closed, allowing second transfer bus 344 to bepowered from supplemental power system converter 340.

In some implementations, the supplemental power system outputselectrical power to the power distribution system when first and secondmain generators 302 and 304 are both operating (e.g., first and secondsupplemental generators 336 and 338 are continuously operated). In anexample implementation, the main power system is configured to providesufficient power for all of electrically powered loads 310 and 310Aunder normal operating conditions, but not enough power for all loads310 and 310A during peak power demand situations without load shedding.The supplemental power system is configured to provide an amount ofpower at least greater than the difference between the main powersystem's maximum power output and the peak power demand of all loads 310and 310A. In other implementations, the main power system is configuredto provide a power output that is insufficient to power all loads 310and 310A and the supplemental power system is configured to provide acombined power output greater than the difference between the maximumpower output of the main power system and the peak power demand for allloads 310. Implementations in which the supplemental power systemsupplements (rather than only backing up) the main power system permitoptimizing of the size of first and second main generators 302 and 304.

First supplemental generator 336 is mechanically coupled to and drivenby first engine 314 and second supplemental generator 338 ismechanically coupled to and driven by second engine 316. FIG. 2 includesa simplified diagram of the mechanical connection of first supplementalgenerator 336 to gearbox 317 of first engine 314. Second supplementalgenerator 336 is similarly connected to second engine 316 via a gearbox317. First and second supplemental generators 336 and 338 are directly(i.e., without a mechanical transmission system to provide speedregulation) connected to the gearboxes 317 of their respective engines314 and 316. Because the speed of first and second engines 314 and 316varies as the aircraft is operated, the speed at which supplementalgenerators 336 and 338 are operated is varied. The AC output ofsupplemental generators varies in magnitude and frequency as the speedof first and second engines 314 and 316 is varied.

The variable output from first and second supplemental generators 336and 338 is input to power conversion system 340. Power conversion system340 converts the variable magnitude, variable frequency input to anoutput with a substantially constant magnitude and frequency. Powerconversion system 340 converts the input to an AC output with amagnitude and frequency that substantially matches the magnitude andfrequency of the AC output from first and second main generators 302 and304.

Power conversion system 340 is configured to selectively couple powerfrom first and second supplemental generators 336 and 338 to the powerdistribution system. More particular, the output of power conversionsystem 340 is selectively coupled to first transfer bus 342 and secondtransfer bus 344 through converter circuit breakers 346. As will bedescribed in more detail below, power conversion system 340 includes aselector 424 for selectively coupling the input from first supplementalgenerator 336 to first transfer bus 342, second transfer bus 244, orfirst and second transfer buses 342 and 344. The input from secondsupplemental generator 338 is selectively coupled by the selector tosecond transfer bus 344, first transfer bus 342, or first and secondtransfer buses 342 and 344. First transfer bus 342 is selectivelycoupleable (via transfer bus breaker 348) to first distribution bus 306,and second transfer bus is selectively coupleable (via transfer busbreaker 350) to second distribution bus 308. First and second transferbuses 342 and 344 are selectively coupled together by transfer tiebreakers 352.

A controller 354 controls operation of power conversion system 340.Controller 354 may be a dedicated power conversion system controller ormay be part of another controller, such as a power system 300controller. Controller 354 controls operation of power conversion system340 to convert the variable input from supplemental generators 336 and338 to the fixed frequency and fixed magnitude output of conversionsystem 340. Controller 354 also controls the selector to controlselective coupling of its input to the transfer buses 342 and 344. Insome implementations, controller 354 controls one or more of thebreakers/contactors 320A, 346, 348, 350, and 352.

Controller 354 is and/or may be implemented in a computing device.Controller 354 includes a processor 356 and a memory 358. Generally,memory 358 stores instructions that, when executed by processor 356,cause controller 354 to operate as described herein. It should beunderstood that the term “processor” refers generally to anyprogrammable system including systems and microcontrollers, reducedinstruction set circuits (RISC), application specific integratedcircuits (ASIC), programmable logic circuits, and any other circuit orprocessor capable of executing the functions described herein. The aboveexamples are exemplary only, and thus are not intended to limit in anyway the definition and/or meaning of the term “processor.” Memory 358may include, but is not limited to only include, non-volatile RAM(NVRAM), magnetic RAM (MRAM), ferroelectric RAM (FeRAM), read onlymemory (ROM), flash memory and/or Electrically Erasable ProgrammableRead Only Memory (EEPROM). Any other suitable magnetic, optical and/orsemiconductor memory, by itself or in combination with other forms ofmemory, may be included in memory 354. Memory 354 may also be, orinclude, a detachable or removable memory, including, but not limitedto, a suitable cartridge, disk, CD ROM, DVD or USB memory.

FIG. 3 is a diagram of an implementation of a supplemental electricalpower system 400 for use in the electrical power system 300 shown inFIGS. 1 and 2. Common components are identified by the same referencenumbers and function in substantially the same manner unless otherwisespecified.

In electrical power system 400, power conversion system 340 includes afirst branch 402 and a second branch 404. First and second branches 402and 404 are substantially identical. Each branch 402 and 404 includes apower converter and may be referred to as a first power converter and asecond power converter. More specifically, each branch 402 and 404includes a rectifier 406, an input filter 408, an inverter 410, and anoutput filter 412. The output of first supplemental generator 336 iscoupled to a first input 416. The output of second supplementalgenerator 338 is coupled to a second input 418.

First and second inputs are coupled to rectifiers 406 in first branch402 and second branch 404, respectively. Rectifiers 406 are any suitablecircuit for rectifying a varying AC output of supplemental generators336 or 338 to a substantially direct current (DC) output. In someimplementations, rectifier 406 includes one or more diodes. Eachrectifier 406 has an input side 420 and an output side 422. Each inputside 420 is connected to first or second input 416 or 418.

Output sides 422 of rectifiers 406 are connected to input filters 408.Input filters 408 smooth out the rectified input to conversion system340 before providing the filtered input to inverters 410. Input filters408 may be any filter suitable for filtering a substantially DC input.Inverters 410 receive a filtered DC input from input filters 408 andconvert the input to an AC output. Inverters 410 may be any invertertopology suitable for converting a DC input to an AC output. The outputfrom each inverter 410 is coupled to output filter 412 for filteringprior to being output through a first output 421 and a second output 423to be coupled (via transfer buses 342 and 344) to the aircraft'selectrical distribution system. Alternatively, the output filter 412 maybe implemented in separate parts to filter differential mode and commonmode noise on the power lines due to inverter 410 switching. In someimplementations, the input and output common mode or differential modefilter components may be combined. In other implementations, the amountof filtering may be reduced or eliminated.

A selector 424 is connected between the first and second branch to allowselective connection (such as under the control of controller 354) offirst and second inputs 416 and 418. Thus, the output of firstsupplemental generator 336 may be connected to first branch 402 or, ifinputs 416 and 418 are connected by selector 424, to first and secondbranches 402 and 404. Similarly, the output of second supplementalgenerator 338 may be connected to second branch 404 or to second branch404 and first branch 402. Selector 424 permits first branch 402 andsecond branch 404 to each receive an input from a separate power source(one of generators 336 or 338), to both operate in parallel with aninput from only one power source, or to operate in parallel with acombined input from both power sources. In the exemplary implementation,selector 424 includes a DC tie 426. Controller 354 is communicativelycoupled to DC tie 426 and can close DC tie 426 to connect first andsecond inputs 416 and 418 or open DC tie 426 to separate first andsecond inputs 416 and 418. In other implementations, selector 424includes one or more power contactors, switches, relays, switchgear,semi-conductor switches, or any other suitable power switching device.

FIG. 4 is a diagram of an implementation of another supplementalelectrical power system 500 for use in the electrical power system 300shown in FIGS. 1 and 2. Common components are identified by the samereference numbers in FIGS. 1-4, and function in substantially the samemanner unless otherwise specified.

In power system 500, selector 424 is located on the input side 420 ofrectifiers 406. Selector 424 is coupled to first branch 402 betweenfirst input 416 and first supplemental generator 336 and is coupled tosecond branch 404 between second input 418 and second supplementalgenerator 338. Thus, the input to selector 424 in system 500 is theunrectified, AC output of generators 336 and 338. First generator 336 iscoupled to first branch 402 through a first backup generator circuitbreaker 502. Second generator 338 is coupled to second branch 404through a second backup generator circuit breaker 504. Tie breaker 506is connected between first and second backup generator circuit breakers502 and 504. By opening and closing tie breaker 506, controller 354selectively couples together first and second inputs 416 and 418. Afirewall 508 separates first and second branches 402 and 404 from eachother and from tie breaker 506.

With reference to FIGS. 5 and 6, implementations of the disclosure maybe described in the context of an aircraft manufacturing and servicemethod 600 (shown in FIG. 5) and via an aircraft 602 (shown in FIG. 6).During pre-production, including specification and design 604 data ofaircraft 602 may be used during the manufacturing process and othermaterials associated with the airframe may be procured 606. Duringproduction, component and subassembly manufacturing 608 and systemintegration 610 of the aircraft 602 occurs, prior to aircraft 602entering its certification and delivery process 612. Upon successfulsatisfaction and completion of airframe certification, aircraft 602 maybe placed in service 614. While in service by a customer, aircraft 602is scheduled for periodic, routine, and scheduled maintenance andservice 616, including any modification, reconfiguration, and/orrefurbishment, for example.

Each portion and process associated with aircraft manufacturing and/orservice 600 may be performed or completed by a system integrator, athird party, and/or an operator (e.g., a customer). For the purposes ofthis description, a system integrator may include without limitation anynumber of aircraft manufacturers and major-system subcontractors; athird party may include without limitation any number of venders,subcontractors, and suppliers; and an operator may be an airline,leasing company, military entity, service organization, and so on.

As shown in FIG. 6, an aircraft 602 produced via method 600 may includean airframe 618 having a plurality of systems 620 and an interior 622.Examples of high-level systems 620 include one or more of a propulsionsystem 624, an electrical system 626, a hydraulic system 628, and/or anenvironmental system 630. Any number of other systems may be included.Although an aircraft example is shown, the principles of the inventionmay be applied to non-aviation industries, such as the automotiveindustry.

Apparatus and methods embodied herein may be employed during any one ormore of the stages of method 600. For example, components orsubassemblies corresponding to component production process 608 may befabricated or manufactured in a manner similar to components orsubassemblies produced while aircraft 602 is in service. Also, one ormore apparatus implementations, method implementations, or a combinationthereof may be utilized during the production stages 608 and 610, forexample, by substantially expediting assembly of, and/or reducing thecost of assembly of aircraft 602. Similarly, one or more of apparatusimplementations, method implementations, or a combination thereof may beutilized while aircraft 602 is being serviced or maintained, forexample, during scheduled maintenance and service 616.

The exemplary power systems described herein include a main power systemand a supplemental power system. The supplemental power system mayfunction as both a backup power system for the main power system and asupplement to the main power system. Thus the example implementationsmay allow smaller main power generators to be used in aircraft. Reducingthe size of the main power generators reduces the weight of the aircraftand redistributes the load on the aircraft's engines, and therebyincreases the efficiency of the aircraft.

The methods and systems described herein are not limited to the specificimplementations described herein, but rather, components of the systemsand/or steps of the methods may be utilized independently and separatelyfrom other components and/or steps described herein.

The description of the different advantageous implementations has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the implementations in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different advantageousimplementations may provide different advantages as compared to otheradvantageous implementations. The implementation or implementationsselected are chosen and described in order to best explain theprinciples of the implementations, the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various implementations with various modifications as are suited tothe particular use contemplated. This written description uses examplesto disclose various implementations, which include the best mode, toenable any person skilled in the art to practice those implementations,including making and using any devices or systems and performing anyincorporated methods. The patentable scope is defined by the claims, andmay include other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal languages of the claims.

What is claimed is:
 1. A supplemental electrical power system for use ina twin engine aircraft having a first and a second main generator drivenby a first and second engine, the first and second main generatorscoupled to provide power to a power distribution system in the aircraft,said supplemental electrical power system comprising: a firstsupplemental generator driven by the first engine; a second supplementalgenerator driven by the second engine; a first power converter includinga first input and a first output, said first input coupled to the firstsupplemental generator, said first output coupled to the powerdistribution system; a second power converter including a second inputand a second output, said second input coupled to the secondsupplemental generator, said second output coupled to the powerdistribution system; and a selector connected between said first andsecond power converters to permit selective connection of said first andsecond inputs.
 2. A supplemental electrical power system in accordancewith claim 1, wherein said first power converter comprises a firstrectifier coupled between said first input and said first output, andsaid second power converter comprises a second rectifier coupled betweensaid second input and said second output.
 3. A supplemental electricalpower system in accordance with claim 2, wherein said selector isconnected to said first power converter between said first rectifier andsaid first output, and connected to said second power converter betweensaid second rectifier and said second output.
 4. A supplementalelectrical power system in accordance with claim 3, wherein saidselector comprises a direct current tie contactor.
 5. A supplementalelectrical power system in accordance with claim 2, wherein said firstpower converter comprises a first inverter coupled between said firstrectifier and said first output, and said second power convertercomprises a second inverter coupled between said second rectifier andsaid second output.
 6. A supplemental electrical power system inaccordance with claim 1, wherein said selector is connected to saidfirst power converter between said first input and said firstsupplemental generator, and connected to said second power converterbetween said second input and said second supplemental generator.
 7. Asupplemental electrical power system in accordance with claim 6, whereinsaid selector comprises a first circuit breaker coupled between saidfirst input and said first supplemental generator, a second circuitbreaker connected between said second input and said second supplementalgenerator, and an alternating current contactor coupled between saidfirst and second circuit breakers.
 8. A supplemental electrical powersystem in accordance with claim 1, further comprising a controllercommunicatively coupled to said selector and configured to operate saidselector to control a flow of power between said first and secondsupplemental generators and said first and second power converters.
 9. Asupplemental electrical power system in accordance with claim 1, whereinsaid first and second generators are continuously coupled to said firstand second engines to provide power to supplement and back-up the firstand second main generators.
 10. A power conversion system for anelectrical power system in a twin engine aircraft having a firstgenerator and a second generator, said power conversion systemcomprising: a first branch including a first input, a first powerconverter, and a first output configured for coupling to an aircraftelectrical distribution system; a second branch including a secondinput, a second power converter, and a second output configured forcoupling to the aircraft electrical distribution system; and a selectorcoupled between said first branch and said second branch, said selectorconfigured to selectively connect the first generator to said firstbranch or said first and second branches, and to selectively connect thesecond generator to said second branch or said first and secondbranches.
 11. A power conversion system in accordance with claim 10,wherein said first power converter comprises a first inverter, saidsecond power converter comprises a second inverter, said first branchcomprises a first rectifier having an input side coupled to said firstinput and an output side coupled to said first inverter, and said secondbranch comprises a second rectifier having an input side coupled to saidsecond input and an output side coupled to said second inverter.
 12. Apower conversion system in accordance with claim 11, wherein saidselector comprises a direct current tie contactor coupled between thefirst and second rectifier output sides.
 13. A power conversion systemin accordance with claim 11, wherein said selector is coupled betweensaid first and second rectifier input sides.
 14. A power conversionsystem in accordance with claim 13, wherein said selector comprises afirst circuit breaker coupled to said first rectifier input side, asecond circuit breaker coupled to said second rectifier input side, andan alternating current contactor coupled between said first and secondrectifier input sides.
 15. An electrical power system for use in a twinengine aircraft having a first engine, a second engine, and a pluralityof electrically powered loads, said electrical power system comprising:a first main generator driven by the first engine and coupled to a powerdistribution system; a second main generator driven by the second engineand coupled to the power distribution system, said first and second maingenerator having a combined output power less than a maximum powerrequirement of the plurality of electrically powered loads; a firstsupplemental generator driven by the first engine; a second supplementalgenerator driven by the second engine, the first and second supplementalgenerators having a combined supplemental output power greater than adifference between the combined output power of said first and secondmain generators and the maximum power requirement of the plurality ofelectrically powered loads; and a power conversion system coupled tosaid first and second supplemental generators, said power conversionsystem configured to selectively couple power from said first and secondsupplemental generators to the power distribution system.
 16. Anelectrical power system in accordance with claim 15, wherein said powerconversion system comprises: a first power converter; a second powerconverter; and a selector connected between said first and second powerconverters to selectively couple power from said first and secondsupplemental generators to said first and second power converters. 17.An electrical power system in accordance with claim 16, wherein saidfirst power converter comprises a first rectifier and a first inverter,and said second power converter comprise a second rectifier and a secondinverter.
 18. An electrical power system in accordance with claim 16,wherein said selector comprises at least one contactor configured forselectively coupling power from said first supplemental generator tosaid first power converter or said first and second power converters,and for selectively coupling power from said second supplementalgenerator to said second power converter or said first and second powerconverters.
 19. An electrical power system in accordance with claim 16,wherein said first main generator is coupled to a first bus of the powerdistribution system, said second main generator is coupled to a secondbus of the power distribution system, an output of said first powerconverter is selectively coupled the first bus, and an output of saidsecond power converter is selectively coupled to the second bus.
 20. Anelectrical power system in accordance with claim 15, wherein said firstand second power converters have a combined supplemental output powergreater than a power requirement of a predetermined subset of theplurality of electrically powered loads.